The present invention relates to an automatic transmission control apparatus, an automatic transmission control method and a recording medium with a program for the method recorded thereon.
Conventionally, in a vehicle equipped with an automatic transmission, the rotation generated by the engine is transmitted to a transmission mechanism, in which gear shifting is performed, and the rotation after the gear shifting is transmitted to a drive wheel to make the vehicle travel.
Automatic transmissions include standard (discontinuously variable) transmissions and continuously variable transmissions. In a standard discontinuously variable transmission, the gear ratio of the transmission mechanism is changed by changing the combination of a gear element for inputting rotation to a planetary gear unit and a gear element for outputting rotation from the planetary gear unit or the like. In the continuously variable transmission, a belt is stretched between a primary pulley and a secondary pulley so that the gear ratio of the transmission mechanism is continuously changed by changing the radial position of the belt on the primary and the secondary pulley, namely, changing the effective diameter of the pulleys. Consequently, the primary pulley and the secondary pulley are provided with a fixed sheave and a movable sheave, respectively, and the effective diameter of each is changed by axially shifting each movable sheave by a driving means as a hydraulic servo, an electric motor or the like.
In the continuously variable transmission, when the belt pinching pressure is high, torque transmission efficiency becomes low. While the belt pinching might be lowered, when the belt pinching pressure is lowered the torque transmitted in the continuously variable transmission may vary over a larger range than suitable when the vehicle encounters bumps on a rough road, or when the accelerator pedal is depressed suddenly. As a result slippage occurs between the primary pulley or the secondary pulley and the belt, and the primary pulley, the secondary pulley and the belt wear to remarkably lower the service life of the continuously variable transmission.
Therefore, the pinching pressure is increased by a certain allowance to prevent slippage from occurring. Where the allowance is m, and the torque to be input to the continuously variable transmission or input torque is T1, the allowance m is set to:
M=(axe2x88x921)xc3x97T1
Wherein a is a constant, and the constant a is determined, for example, to be 1.04.
A continuously variable transmission in which the allowance m can be changed according to the driving state, driven state or the like of an engine has been disclosed in Japanese Patent Publication No. HEI 6-288448.
In the aforementioned conventional continuously variable transmission, as the pinching pressure is always higher by the allowance m, the torque transmission efficiency is lowered accordingly.
It is an object of the present invention to provide an automatic transmission control apparatus, an automatic transmission control method, and a recording medium with a program for the method recorded thereon, which solve the problems of the conventional continuously variable transmission, which improve durability of a continuously variable transmission, and which increase the torque transmission efficiency.
Accordingly, the present invention provides an automatic transmission control apparatus which includes a primary pulley, a secondary pulley, a belt stretched between the primary pulley and the secondary pulley, pinching pressure generation means for generating a belt pinching pressure, travel environment detection means for detecting a travel environment of a vehicle, torque variation estimation processing means for estimating the transmission torque variation during travel, and pinching pressure change processing means for changing the pinching pressure based on the estimated results.
In this case, since the transmission torque variation during travel is estimated and the belt pinching pressure is changed based on the estimation, the pinching pressure is prevented from constantly increasing. Accordingly, torque transmission efficiency can be increased and fuel consumption can be improved.
Since the pinching pressure is regulated to correspond to the travel environment, slippage is prevented from occurring between the primary pulley or the secondary pulley and the belt. Consequently, the primary pulley, the secondary pulley and the belt are prevented from wearing and the durability of the continuously variable transmission is thereby improved.
In a preferred embodiment of the automatic transmission control apparatus of the invention, the pinching pressure change processing means increases the belt pinching pressure when the transmission torque tends to vary greatly and lowers the belt pinching pressure when the transmission torque hardly varies.
The torque variation estimation processing means may estimate the transmission torque variation based on the change of a shift schedule selected based on the travel environment or based on the travel area.
The torque variation estimation processing means may estimate that the transmission torque hardly varies in a travel environment for which it is estimated that a sudden change of throttle opening will not occur, e.g., a congested road, a downhill road, or an expressway.
In a preferred embodiment of the automatic transmission control apparatus of the invention, furthermore, the travel environment includes at least a travel area and the driving state. The torque variation estimation processing means estimates the transmission torque variation based on at least either the travel area or the driving state.
In one embodiment of the automatic transmission control apparatus of the invention, the torque variation estimation processing means estimates that the transmission torque will tend to vary easily in a travel environment where it is estimated that the throttle will be open a medium to high degree and the accelerator will be turned on and off frequently.
The travel environment where it is estimated that the throttle will be open a medium to high degree and the accelerator will be turned on and off frequently may be, for example, a mountain road or an uphill grade.
In another preferred embodiment of the automatic transmission control apparatus of the invention, the torque variation estimation processing means estimates that the transmission torque will hardly vary in a travel environment where it is estimated that there is a small possibility of sudden acceleration, for example, where there is no vehicle ahead during travel on an expressway and where there is a vehicle ahead during a stop.
In still another preferred embodiment automatic transmission control apparatus of the invention, the torque variation estimation processing means estimates that the transmission torque will tend to vary easily in a travel environment where it is estimated that there is a large possibility of sudden acceleration, for example, where there is a vehicle ahead during travel on an expressway.
Preferably, the travel environment includes at least a road surface condition and the torque variation estimation processing means estimates the transmission torque variation based on the road surface condition.
In another embodiment of the automatic transmission control apparatus of the invention, the torque variation estimation processing means estimates that the transmission torque will tend to vary easily in a travel environment where it is estimated that the reaction force received from the road surface will be large, for example, where the road surface is a gravel road surface or an ice and snow-covered road surface.
Preferably, the torque variation estimation processing means estimates that the transmission torque will hardly vary in a travel environment where it is estimated that the reaction force received from the road surface will be small, e.g., a smoothly frozen road surface.
In still another embodiment of the automatic transmission control apparatus of the invention, the travel environment detection means detects the travel environment based on operation information.
The control method of the present invention comprises the steps of detecting travel environment of the vehicle, estimating the transmission torque variation during travel based on the detected travel environment, and changing the belt pinching pressure based on the results of the estimation.
The present invention also provides a machine readable medium having, encoded thereon, a program for the automatic transmission control method which detects a travel environment of the vehicle, estimates the transmission torque variation during travel based on the detected travel environment, and changes the belt pinching pressure based on the results of the estimation.